I've read on other threads (cant remember where) that people have withdrawn during orientation. People objected but I dont know if that is just a matter of ethics. But, should you rearrange your life for other people's ethics? I can tell you, I'd rather be able to see my fiance & family & withdraw during orientation than stick out 4 years & put off getting married bc of other people's ethical reasons. I would say, find out from the school you plan to attend what the financial penalty is (tution-wise) for withdrawing in the first week.
If you have an offer from school X & you begin school Y, how can school Y tell you that you are not allowed to withdraw--you already have the offer from X so what are you worried about. Just my opinion--I could be wrong, you should check it out.